TV troubles :(

I'm really annoyed, there is something wrong with our brand new tv!! And of course, we already got rid of the packaging and I can't find the receipt anywhere (but neither of us remember throwing it away), not that Target would probably take it back without a package, but its always worth trying. So, I decided to call on the warranty and on their website, they are going to want us to mail in the tv (we have to pay for it) and in its original packaging.... I don't see that happening. Its not my fault it doesn't work!! So basically, last night we turned on the TV and we couldn't get sound on all the channels. It was kinda weird, but I figured maybe it was just the cable or something. So when it happens again this morning, I decide to try another co-ax cable, try to plug it into a cable thing that I know works because my other TV uses it, and to even use the cable and the plug that the other TV that works perfectly. So I notice that when I wiggle the co-ax cable in the back of the TV, it will pick sound here and there, so I guess the connection is loose somehow, but I don't know how to fix it. And I don't get why it would all of a sudden do this?? If anyone has any ideas, I'll gladly take them!!! I want my TV to work!